The following meanings for the abbreviations used in this specification apply:
A&F: amplify and forward
AP: antenna port
BER: bit error rate
BS: base station
CAS: cooperation areas
CCE control channel element
CDF: cumulative distribution function
C-MIMO: cooperative multi input multi output
CoMP: coordinated multipoint
COOPA: cooperative antenna
CQI: channel quality indicator
CRS: common reference signal
CSI: channel state information
D&F: decode and forward
DL: downlink
eNB: evolved Node B (eNodeB)
FDD: frequency division duplex
GI: guard interval
HARQ: hybrid automatic repeat request
LOS: line of sight
MS: mobile station
MCS: modulation and coding scheme
MIMO: multiple input multiple output
MU-MIMO: multi user MIMO
NB: NodeB
OFDM: orthogonal frequency division multiplexing
OFDMA: orthogonal frequency division multiple access
PDCCH: physical downlink control channel
pDRS: precoded dedicated reference signal)
PDSCH: physical downlink shared channel
PRB: physical resource block
R8: Release 8
RB: resource block
RE: resource element
RNTI: radio network temporary identifiers
RS: reference signal
RRM: radio resource management
RS: reference signal
SC: subcarrier
SDM: spatial division multiplexing
SINR: signal to noise and interference ratio
TDM: time division multiplexing
TDD: time division duplex
UE: User equipment
ZF: zero forcing
The present application relates to, among others and not limited thereon, channel estimation. Channel estimation for broadband mobile radio systems is generally a challenge due to a large time variance and frequency selectivity of the radio channels in case of fast moving UEs. In case of cooperative antenna (COOPA) systems, where a coherent precoding of data signals from different transmission sites is intended, the challenge is even higher due to the higher number of radio channels as well as the required high accuracy with respect to the channel state information (CSI) estimates.
Recently, 3GPP is investigating in the so called LTE Advanced study item techniques to increase performance significantly, and so the called cooperative or coordinated multipoint transmission (CoMP) has been identified as one of the main techniques to increase spectral efficiency. Different CoMP techniques have been identified, where the more powerful ones transmit simultaneously precoded data from different eNBs to several UEs on the same time frequency resource. Coherent precoding—while adding complexity and leading to quite some overhead regarding channel estimation, feedback and backhaul traffic—promise significant performance gains as they allow for optimum interference cancellation and have inherent diversity gains. From theory large gains in the order of several 100% have been predicted.
As LTE advanced is seen as an evolution from LTE Rel. 8, full backward compatibility is generally requested.
This, however, poses problems in particular in connection with CoMP, since the techniques used for CoMP partly contradict to those techniques currently used, e.g., in LTE Rel. 8.
Furthermore, there occurs a problem that in connection with different kinds of reference signals (such as channel state information (CSI) reference signals (RS), predecoded dedicated reference signals (pDRS, also known as demodulation reference signal DM-RS) and common reference signals (CRS)), a large overhead might be produced, which compromises the improvements achieved by CoMP.
In addition, the above problems may also occur in other coordinated transmission techniques than CoMP, e.g., in MU-MIMO (multi user multiple in multiple out) etc.